1. Field of the Invention
The present invention relates to the field of surveying and more particularly to a rapid, automatic and accurate apparatus for surveying grid locations over an area including the mapping details of underground iron pipelines, and more particularly the location of bell joints.
2. Description of the Prior Art
Currently in the art the time of signal arrival, trilateralization, differential time of arrival or other techniques are used to solve for the present location of a mobile station, based on receipt of the transmitted signals and weighting of received signals. A previous patent describing a laser beam measurement system is found in U.S. Pat. No. 5,000,564. This patent describes a laser beam three dimensional measurement system wherein the range of the receiver from the transmitter and the angular position of the receiver are determined by the receiver without interaction of the transmitter. The receiver range is determined trigonometrically by measuring the incident angle of the laser beam at two locations on the receiver.
U.S. Pat. No. 4,030,832 describes a grade rod and method of use in a surveying system employing a laser beam which is rotated in a plane. This surveying system is used for measuring elevation and grades. The grade rod includes a graduated scale on a moveable tape connected with a light detector such that the tape and the detector are automatically controlled in their movement.
While the prior art describes ways to survey a given land location, using therein described apparatii is time consuming. There is interest in the surveying industry to quickly survey a location. The prior art does not use an absolute reference or control for measuring a location. Instruments and methods of the prior art require considerable time to perform accurate measurements. This invention overcomes the time consuming processes of the prior art by allowing for quick data collection of survey points over an area.
Previous methods of seeing objects buried underground include the reflection of microwave photons. The scattering and absorption of photons in this wavelength range due to the covering aggregate, and moisture variations in the ground, leads to poor resolution of details when using ground penetrating radar equipment. In the case of buried iron pipes it is the ferromagnetic nature of this material that offers an alternative possibility of sensing details through the measurement of magnetic fields. This invention provides for a detailed map of the magnetic field with reference to the stationary unit. Hidden ferromagnetic objects and depth information can then be obtained.
For use in the field, the invention should be rugged and lightweight, and self-contained such that it should not require connection to a power source. Further it should be user-friendly, presenting reliable and accurate information rapidly. The invention provides for a reference unit in place whereby comparisons can be made to establish accurate data, such as survey points to make a grid, temperature measurements, and terrestrial field perturbation measurements including temporal fluctuations.
An object of the present invention is to provide a rapid and accurate means for surveying a location. An apparatus for precision grid surveying has a stationary unit holding a light source unit that emits a light beam. The light source unit has a rotator that projects the light beam toward a roving unit with a photodetector There is a roving unit for moving the photodetector over a plane. The light beam can be a parallel beam or a laser. The rotator rotates the light beam about a vertical axis such that the light beam sweeps in a horizontal plane at a steady angular frequency.
The rotator comprises at least one mirror at 45 degree angle and a motor unit wherein the mirror is rotated by the motor unit.
A first clock is on the roving unit and a second clock is on the stationary unit. The first and second clocks are synchronized such that the time is measured when the light beam is intercepted by a detector, and is referenced to the instantaneous orientation of the mirror.
The roving unit has three photodetectors to intercept the light beam at sequential instances of time. These photodetectors may be non-collinear. The roving unit can be a cart with wheels. The apparatus may further comprise means for measuring the magnitude of the terrestrial magnetic field in two dimensional grid plane and digital means for recording and storing the measurements.
A method of precision grid surveying using the above apparatus comprises the steps of placing the stationary unit outside an area to be surveyed; moving the roving unit across the area such that the detectors detect the light beam; and collecting data from the detection means. The method may further comprise the method of mapping hidden ferromagnetic structures by also measuring magnitude of a terrestrial magnetic field in a two dimensional grid plane at said stationary point and said roving point; subtracting from said roving point magnitude measurement said stationary point magnitude measurement; correcting for a temporal field fluctuation by measuring and subtracting the temporal field fluctuations; recording and storing the measurements by digital means and finding the location and structure of buried ferromagnetic objects by analyzing the measurements for deviations from uniformity.
The instrument is independent of the properties of the covering ground such as inhomogeneities caused by the presence of rocks or moisture or boundaries between clay and sand. Another object of the present invention is to provide a method and instrument which can map details of hidden underground iron pipelines, more particularly the location of bell joints, so as to avoid unnecessary excavations. The instrument is user-friendly, presenting reliable and accurate information rapidly in a form that is directly related to finding the correct place to excavate.